Process and apparatus for annealing and tempering metals.



strasse,

' HEINRICH 'KRnUTSCHNEIDE-R, or m nus, GERMANY,

PROCESS AND APPARATUS FOR- ANNI ALING AND TEMPERING MIETLLS.

To all whom it may concern:

Be it known that I, Hammer! Kaiser- SCHNEIDER, engineer, a subject ofthe German Em eror, residing at Berlin, Culinermany, have invented acertain new and useful Process and anAp aratus for Annealing and Tomering Meta s. and Metallic Products and l do hereby declare thefollowing to be a full, clear, and exact description of the invention,such as will enable others skilled in the art to which it apper tains tomake and use the same.

In the treatment of metals and metallic products, uniform annealing ofsuch products at a certain temperature which must be maint ained exactlyconstant, plays a very important )art. Thus, for instance, in temperingsteel or other alloys that can be tempered, the maintenance'of the exacttem erature and' uniform distribution of the mat over single pieces tobe annealed or tem ercd is of the utmost importance. Unequal leating ofpieces of metal with unsymmetrical cross sections leads to contrae 1011of the heated parts during the cooling, giving rise to internal strainsetc.

Furnaces of all kinds do not su'fiiciently insure uniform heating ortempering above purpose. The well-known method of heating the articlesto be tempered in fusible baths of metallic salts, metallic oxids andsimilar metallic com ounds has the great advantage in princip e ofroviding for free heating by radiation. T e application of this processof annealing or tempering by means of fusible baths presents howevergreat practical difliculties. In order by external heating to raise, thetemperature of the bath consisting of metallic salts or the in like, tothe extent required, that is to say to 8005-870. (l the method nowemployed is to expose iron vessels (crucibles etc.) filled with fusibleflux to direct heating in furnaces. Owing to the high temperature to 5which the outer walls of the cruc bles are ex posed the metal of whichthe crucibles are v composed is soon destroyed and such destruction isaccelerated on the one side by the action of the combustion gases and onence of the flux. In addition to this, it must be remembered thatannealing furnaces of this kind are ver inefiicient as regards theconsumption of temperature of annealing to be regulated in for the theother side by the generally oizidizing influ-- uel, and do not allow theSpecification of Letters Patent. Application filed July 7, 1904. SerialNo. 215,588.

l i I cant extent.

Patented Sept. 22, 1908 the exact and reliable manner required for theurpose in question.

T is invention relates to an annealing process in which the abovedrawbacks are obviated, and to an apparatus for carrying out saidprocess. According to this process, the article to be tempered orannealed is heated to the desired temperature in a nonmetnllic fusiblebath heated directly by electric currents of sufiicicnt strength.

The advantages of this annealing process are obvious. First of all, itis possible to regulate the temperature electrically in a veryconvenient manner; then loss of heat can 'be reduced to a minimum tric.heating, and finallythe current used in the furnace serves as an exactmeasure of the temperature of the fusible flux, as the con.- ductivityof the latter increases very quickly with the temperature. .In carryingout this process, it is preferable to use furnaces made of refractorymaterial which is not dissolved by the molten flux (such as anagncsiteor the like). The walls of the furnace must at the same time be pro erlyinsulated, so as to prevent radiation oi heat outwards. For prei cntingradiation losses, 7 the furnace is preferably closed at the to exceptfor a charginmopening through which the articles to e annealed areintroduced and removed.

The heating of the flux, which must take place before the furnace isstarted, so as to get sufficient conductivity, is cilcctcd by electriccurrent of sufficient strength su plied by means of suitable electrodes.T ie electrodes must be made of some-material which is a sufficientlygood conductor and which is refractory such for instance as iron,carbon, etc. The electrodes are arranged in the furnace in suchpositions as to result in uniform heating of the bath by the current.

The bath preferably consists of substances which do not chemicallyattack the articles to be tempered, or'at least to a very insigmfi- 1Baths can also be used which at the temperature in question can yieldcar'- bon to the articles to be annealed, and thus increase theircontents of carbon, as for instance in the case of steel. Some of thesub- 1 stances which may be used to yield carbon to the article to beannealed are oxalate of calcium and carbids of various metals.

Suitable substances which can be used for the fusible oath are fiuorids,carbids, car- 1 by this internal slee 7 .l i i l l fo'r the purposes ofmy invention. By the term non-inetallic bath, I mean baths such asbonates, etc, such fluxes having at the terns perature in question. 'acomparatively great cubic centimeter.

For the purgose of defining the bath empleyed 'by'me, have desi ated thesame as anon-metallic bath, there y excluding baths of molten' metalwh'ch would be inoperative hereinbefore specified or suchas are similar1n composition or effect.

, If the flux is basic, the material '0: which thefurnace is made mustalso be basic; if

the flux is acid, it mustbe also acid, so as not to be attacked by theflux.

' The electrodes are preferably arranged interchangeably so that the'iymay be replaced by new ones when corro ed after a certain amount of use,as such corrosion cannot be avoided. It is preferable to use alternatingcurrent for heating, so as to avoid'electroly sis in the bath.

For regulating the strength of the current in the latter'case,transformers could be used withhdjustable primary winding, and alsochoking coils.

What I claim as my invention and desire to secure by Letters Patent is:p

1. The herein described process of heating metals, which consists in,inserting the objects to be heated in a fusible non-metallic bath heatedby an electric current, and regulating sa 1d current to maintain thebath at the required temperature, the current passing throu h both thebath and the immersed portion 0 said ob'ects 2. The herein escribedprocess of heating metals, which consists in producing a moltennon-metallic bath by means of an electric current, inserting the objectsto be heated in .said bath, and maintaining the required temperature ofthe bath by regulating the said heatin current, the current passingthrough bot the bath and the immersed portion of said objects.

3. The herein described process of heating metals, which consists ininsertin the objects to be heated into a fused bath ormed of a conductorwhose conductivity increases with the temperature, and passing anelectric current through said bath, and thereby heating said objects tothe desired temperature.

4.. The herein described process of heating metals, whichconsists ininserting the objects to be heated into a fused non-metallic bath, andpassing an electric current through said bath, whereby the temperatureof the bath is maintained, and also passing the current through the"objects themselves, whereby their resistance also serves as a heatingmeans. w

5. The herein described process which consists in introducing iron orsteel articles into an electrically heated fusible non-metallic bathwhich yields carbon to the article.

6. A bath for heating metals, to any desired temperature up to a whiteheat, while retaining said metals solid, consisting of fused conductivematerial whose conductivity increases with increase of its tem erature,said material being inert tower the metal to be heated, and means forpassing an alternating current throu h said bath.

In testimony whereof, %have hereunto set my hand and affixed my seal,inthe presence of the two subscribing witnesses.-

HEINRICH KRAUTSCHNEIDER. [n.a]

Witnesses:

WOLDEMAR Ham,

HENRY Hasran.

